Erroneous conductivity readings with ADuCM3029_demo_cn0428_cn0429

  • We are getting erroneous conductivity readings with ADuCM3029_demo_cn0428_cn0429.
  • This is with the latest hex file downloaded 4/1/2021.
  • We are using standard solution KCL-700, a 700 microsiemens solution.
  • We are using the recommended probes - Cole-Parmer 100-series Replacement Conductivity/Temperature Probe, K=1, 59200-06 probes
  • DIP switches are set to Z mode.
  • Mode is changed to conductivity.
  • We are getting a reading readings like 3e-07 S/cm (screenshot).
  • We should be getting readings like 7e-04 S/cm.

Reference: github.com/.../81

Thanks for your help.

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  • 0
    •  Analog Employees 
    on Apr 20, 2021 3:45 PM in reply to jpagliaccio

    Thanks for the results. The resistor values look correct to me within a percent or so. 1/1.5k ohms is 667 uS.

    So that tells me it's something about the sensor or the way it was connected to the board. A couple things to try:

    • Clean and rinse the sensor as recommended in the instructions sheet that came with the sensor
    • Make sure the contacts are fully submerged in the liquid (you might have to submerge it a little farther than you think because the contacts are sheathed by the plastic for protection)
    • Make sure the bnc is fully connected to the board
    • If that's not it, it may explain the readings if the standard solution is mislabeled and it's actually distilled water or something like that.

    By the way, Hi-Z mode shouldn't work with anything <200k ohms as mentioned in the user guide, so you wouldn't get a valid reading in Hi-Z mode. Essentially the gain of the TIA is too high so the amplifier saturates when there's a low conductivity present. Unfortunately, there's not a good way for the software to tell that the amplifier is saturated in that mode so we can't raise a flag.

    I hope it helps.

    Best regards,
    Scott

  • I did your suggestions and I am still getting values like "Conductivity(S/cm): 1.9979e-06" for KCL-700 solution. Can you tell me what value I should be getting? This is with a Cole-Parmer probe 59200-06. Thanks. 

  • 0
    •  Analog Employees 
    on May 3, 2021 8:04 PM in reply to jpagliaccio

    I'm reminded of a mistake that I made the first time I used one of these sensors. Did you remember to take the end cap off of the sensor? It's not completely obvious that it's there because it's the same color as the probe body, and if the cap is still on, it would prevent liquid from getting to the sensing electrodes.

    Thanks,
    Scott

  • Scott:

    The 59200-06 sensors came with little bottles of 4M Kcl solution attached to the ends. The bottles of solution were removed. There were no end caps. They match the image above. We purchased 2 boards, 2 sensor modules, and 4 probes. None are working.   

    Are these the probes that you have working? 

    Thanks,

    Joe

  • Scott:

    We are making no progress on this and we are considering switching to the EVAL-CN0411-ARDZ and the 

    EVAL-ADICUP360, but I don't see a HEX for that. If we purchase those kits would you be able to provide a hex file for the ADuCM360_demo_cn0411 demo? Optionally working Arduino code would be good too. 

    To be clear we are trying to measure conductivity and ultimately TDS

    Thanks,

    Joe